Environmental particulate matter formed by combustion is composed of an inertcarbonaceous particulate core and layers of adsorbed pollutant molecules. After inhalation and deposition in the lung, a portion of the burden of adsorbed pollutant molecules-those molecules present at greater than one monolayer surface coverages-will be released into pulmonary surfactant. This initial release of particle-adsorbed pollutant molecules occurs rapidly and produces a general acute exposure of the lung parenchyma to the released pollutant molecules. The remaining particulate matter stays on the lung epithelium until it is phagocytized by an alveolar macrophage. Release of the residual burden of adsorbed pollutant molecules at surface coverages of less than one monolayer occurs inside the alveolar macrophage. Polynuclear aromatic hydrocarbons (PAHs) comprise the majority of the molecules present in the first monolayer since both the carbonaceous particles and the PAHs are formed concurrently by similar chemical reactions. The hypothesis of this application is that release of strongly adsorbed pollutant molecules occurs inside the macrophage as the result of chemical reactions with reactive oxyradicals. The environmental health significance of these reactions is that they may cause the activation of some of these molecules to more toxic agents. The specific aims of this application are to: 1. Demonstrate that release of adsorbed PAH molecules, present at surface coverages less than one monolayer on carbonaceous particles, occurs as a result of chemical reactions with reactive oxyradicals inside the alveolar macrophage. 2. Determine the reaction mechanisms responsible for this intra-macrophage release.